The present invention relates to a graphic equalizer which is suitable for audio equipment installed in an automobile, such as a car stereo.
Audio equipment installed in an automobile, in which an AM/FM radio, a tape recorder etc. are assembled together, has been known as a so-called car stereo and has become an almost indispensable equipment for present day automobiles.
In addition, the requirement of audio equipment for high fidelity has extended also to car stereo. As equipment of excellent acoustic characteristics has come into use, scrupulous care has become necessary for the adjustment of acoustic characteristics in a car or the adjustment of a programmed frequency characteristic. Therefore, car stereos have been furnished with graphic equalizers for such purpose.
The graphic equalizer (hereinbelow, termed "GEQ") divides the frequency band of the audio signals into a plurality of frequency bands or channels and changes characteristics in the respective channels, whereby a frequency characteristic over the whole band can be changed at will. In general, GEQs are known which are based on the combination of a bridge amplifier and a simulated inductor employing operational amplifiers. By disposing such a GEQ in a car stereo, the aforementioned requirements can be met.
Since the GEQ is typically provided with a plurality of variable resistors or switches for adjustments in correspondence with the various channels, its operation requires considerable skill. In fact, operation is considerably complicated and troublesome even for a skilled person.
It has accordingly been a considerable burden upon the user that the operations of the GEQ must often be repeated with a change of programs, etc. Especially for car stereos or the like equipment installed in automobiles, the operation has also become very unfavorable from the standpoint of the safety of driving of the automobile.
In order to solve such problems, there has been proposed the so-called presettable GEQ wherein data which correspond to various frequency characteristics intended to be established by the GEQ are set in a memory or the like in advance and wherein any desired frequency characteristic can be afforded merely by the operation of selecting one of the preset data as needs arise.
In a presettable GEQ (hereinbelow, termed "PGEQ"), the necessary equalizing characteristics can be given by disposing it in the car stereo or the like and operating it simply and safely. Therefore, functions of the audio equipment furnished with the GEQ can be fully demonstrated, and the car stereo or the like can be satisfactorily rendered high in performance and high in grade.
On the other hand, however, such prior-art PGEQ affords the equalizing characteristic on the basis of the control datum read out from a memory. Disadvantageously, therefore, it is impossible to know the state of the selected frequency characteristics immediately from the positions of the operating keys on a control panel, as in the conventional GEQ.